Escherichia coli capsular polysaccharides (K antigens) have often been associated with increased virulence (17). The K1 antigen in particular increases the invasiveness of E. coli, and these strains are often involved in cases of meningitis and septicemia (32). These polysaccharide coats also act as recognition sites for bacteriophages, which often carry tail spikes that contain polysaccharide depolymerization activities. Several K1 specific phages have been described (10), one of which, ΦK1E, was found to possess N-acetylneuraminidase (endosialidase) as a part of the tail fiber protein (37). This enzyme catalyzes the cleavage of α-2,8-linked poly-N-acetylneuraminic acid carbohydrate polymer of the K1 capsule. It has been suggested that the tail fiber protein is involved in both adsorption to the cell surface and penetration into the cell by enzymatically degrading the polysaccharide capsule. The ΦK1E endosialidase gene has been cloned and sequenced (20). A similar gene has been cloned and sequenced from ΦK1F (29).
ΦK5 is a related bacteriophage specific for E. coli strains that display the K5 antigen, a polymer consisting of a repeating structure of 4-linked a-N-acetylglucosamine and β-glucuronic acid (N-acetyl heparosin). In this case, ΦK5 encodes a tail associated K5 specific lyase protein that is also responsible for attachment to the cell surface and degradation of the K5 polysaccharide capsule (12,14). Phage have also been found that are specific for other E. coli polysaccharide antigens including K3, K7, K12, K13, and K20 (26,27); all probably possess specific polysaccharide depolymerization activities as part of the phage particle.
Both ΦK5 and ΦK1E have a Salmonella phage SP6-like promoter upstream of their tail proteins as well as a region of sequence similarity, which is just downstream of the lyase gene of ΦK5 and just upstream of the endosialidase gene of ΦK1E (6). The sequences upstream of the tail gene promoters in ΦK1E, and ΦK5 are highly similar as well. ΦK5, ΦK1E and SP6 share a common morphology and life cycle, suggesting that they may be closely related.
Antibiotics superseded the potential use of bacteriophage in the treatment of infections. The extensive use of antibiotics has led to antibiotic-resistant bacterial pathogens. Thus, investigators have reassessed bacteriophage therapy and prophylaxis. However, one major obstacle that is frequently raised to the use of bacteriophage is that of their excessively narrow host range. There is a need for bacteriophage having multiple host-range for use in therapy and prophylaxis.